Driving operation support system and method

ABSTRACT

In deviation prevention support ECU  10  in driving operation support system  1 , an applied torque by steering torque applier  17  is set based on a vehicle speed of a vehicle. The applied torque is set to increase with increase of the vehicle speed. An upper limit according to the vehicle speed is set for this applied torque. Furthermore, in a Start interval in application of the applied torque, a rate of increasing to reach a maximum is determined according to the maximum of the applied torque. In a Close interval, the applied torque is decreased at a rate different from that in the Start interval, and the absolute rate of increasing the torque in the Start interval is set to be larger than the absolute rate of decreasing the torque in the Close interval.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a driving operation support system andmethod and, more particularly, to a driving operation support system andmethod that performs lane deviation prevention support for preventingfrom deviation of a moving vehicle from a lane.

2. Background Art

There are vehicles with a lane deviation preventing function forpreventing a vehicle running on a road with a lane drawn thereon, fromdeviating from the lane. A system provided with this lane deviationpreventing function is, for example, the one disclosed in JP 07-104,850A(hereinafter referred to as Reference 1). This system is configured totrack a center line between boundary lines of a lane, to apply a torqueon the steering mechanism of the vehicle by an electric motor coupled tothe steering mechanism, upon deviating the vehicle from the center line,and thereby return the vehicle toward the position of the center line.

SUMMARY OF THE INVENTION

Incidentally, Reference 1 describes nothing in particular about atemporal pattern and the magnitude of the torque applied on the steeringmechanism. As a conventional method of applying such torque, the appliedtorque was applied in a fixed steer angle pattern and torque pattern.Namely, the torque pattern herein was set with a fixed slope and maximumof applied torque.

However, the control according to such a constant torque pattern posed aproblem that with control in a low vehicle speed range, the driver feltgreat variation of behavior of the vehicle to the control. Furthermore,there were also desires for improvement in a deviation margin time and adriver's response time, and for improvement in the feeling about warningtorque.

An object of the present invention is therefore to provide a drivingoperation support system and method capable of reducing the behaviorfelt by the driver during the control in the low vehicle speed range andimproving the deviation margin time and the driver's response time andalso improving the feeling about the warning torque, in execution of thelane deviation prevention control.

A driving operation support system according to the present invention toachieve the above object is a driving operation support system for, whenlane deviation estimating means estimates that a moving vehicle willdeviate from a lane, applying a warning torque to the vehicle to preventa deviation from lane, wherein a pattern of application of the warningtorque to the vehicle is determined according to a vehicle speed.

In the driving operation support system according to the presentinvention, the applied pattern of the warning torque applied with aestimation that the vehicle will deviate from the lane is determinedaccording to the vehicle speed. By determining the applied pattern ofthe warning torque according to the vehicle speed in this manner, it isfeasible to reduce the behavior felt by the driver during the control inthe low vehicle speed range and to implement the control withimprovement in the deviation margin time and the driver's response timeand with improvement in the feeling about the warning torque.

The driving operation support system can be configured in such a formthat the warning torque is increased with increase in the vehicle speedwhen estimating that the vehicle will deviate from the lane.

By carrying out the control so as to increase the warning torque withincrease in the vehicle speed in this manner, it is feasible to keep theyaw rate small on the vehicle. The driver is thought to feel stronglythe variation of behavior of the vehicle through the yaw rate, and thevariation of the behavior felt in the low vehicle speed range by thedriver can be reduced by keeping the yaw rate small.

The driving operation support system can also be configured in such aform that in the application of the warning torque to the vehicle, thewarning torque is set in such a magnitude that a yaw rate on the vehicleis kept constant.

By setting the magnitude of the warning torque so as to keep the yawrate constant on the vehicle in this manner, it is feasible to furtherreduce the variation of the behavior felt in the low vehicle speed rangeby the driver.

Furthermore, the driving operation support system can also be configuredin such a form that an upper limit is set for the warning torque appliedto the vehicle.

With application of the warning torque according to the vehicle speed,the variation of the behavior felt in the low vehicle speed range by thedriver is reduced on one hand, whereas the driver might feel greatbehavior in the high vehicle speed range on the other hand. Inconnection therewith, if the upper limit is set for the warning torque,the warning torque can be prevented from becoming too large even in thehigh vehicle speed range. Therefore, the behavior variation felt by thedriver can be prevented from becoming too large.

The driving operation support system can be configured in such a formthat the upper limit is the warning torque at a reference vehicle speed.

When the upper limit set for the warning torque applied to the vehicleis set to the warning torque at the reference vehicle speed, it isfeasible to readily set the upper limit of the warning torque applied tothe vehicle.

The driving operation support system can also be configured in such aform that the warning torque increases to its maximum at a specifiedrate responsive to the maximum warning torque applied to the vehicle.

If in the application of the warning torque which increases to itsmaximum at the constant rate, the timing of occurrence of aimed vehiclebehavior will vary. The time up to nullification of the warning torquewill vary in decrease of the warning torque. These problems can beovercome by setting the rate of increasing the warning torque, based onthe maximum warning torque.

Furthermore, the driving operation support system can also be configuredin such a form that the rate of increasing the warning torque is so setthat a time necessary to reach the maximum warning torque is keptconstant.

Where the warning torque is large, a long time is necessary to reach itsmaximum value. This will pose a problem that a sufficient deviationmargin time cannot be secured in the high vehicle speed range. The timenecessary to reach the maximum warning torque can be kept not too longby setting the rate of increasing the warning torque as follows: therate of increasing the warning torque is so set that the time necessaryto reach the maximum warning torque becomes constant based on themaximum warning torque. Therefore, it is feasible to secure a sufficientdeviation margin time in the high vehicle speed range.

Another driving operation support system according to the presentinvention to achieve the above object is a driving operation supportsystem for, when lane deviation estimating means estimates that a movingvehicle will deviate from a lane, applying a warning torque to thevehicle to prevent a lane deviation, wherein in an operation of, afterincrease of the warning torque, decreasing the warning torque increased,the warning torque is decreased at a different absolute rate from thatduring the increase of the warning torque.

Where the absolute rate of increasing the warning torque is equal to theabsolute rate of decreasing the warning torque, it is difficult tosecure the deviation margin time and to eliminate the driver'suncomfortable feeling or the like due to sudden removal of the warningtorque, all together. In this respect, when the absolute rate ofdecreasing the warning torque is set at a different absolute rate fromthat of increasing the warning torque, it is feasible to readilyimplement the control to overcome these problems at once.

The driving operation support system can be configured in such a formthat the absolute rate of increasing the warning torque is set largerthan the absolute rate of decreasing the warning torque.

When the absolute rate of increasing the warning torque is set at alarger value than the absolute rate of decreasing the warning torque, itis feasible to secure a sufficient deviation margin time and to informthe driver of a start of the deviation prevention support by change ofthe steering torque in an early stage. It is also feasible to reduce thedriver's uncomfortable feeling due to sudden decrease of the warningtorque and to moderately resolve the behavior change of the vehicleafter occurrence of the warning torque and before nullification of thewarning torque.

Still another driving operation support system according to the presentinvention to achieve the above object is a driving operation supportsystem for, when lane deviation estimating means estimates that a movingvehicle will deviate from a lane, applying a warning torque to thevehicle to prevent a lane deviation, wherein in an operation ofincreasing the warning torque to a maximum, a rate of increasing thewarning torque in a predetermined first increase period from a start ofthe increase is set larger than a rate of increasing the warning torquein a second increase period subsequent to the first increase period.

In this configuration, the period from the start of applying the warningtorque to reaching the maximum torque is divided into the first increaseperiod and the second increase period, and the rate of increasing thewarning torque in the first increase period is set larger than that inthe second increase period, whereby it is feasible to initiate thevehicle behavior for lane deviation prevention in an early stage.

The driving operation support system can also be configured in such aform that in an operation of decreasing the warning torque from themaximum, a rate of decreasing the warning torque in a predeterminedfirst decrease period from a start of the decrease is set larger than arate of decreasing the warning torque in a second decrease periodsubsequent to the first decrease period.

In this configuration, the period from application of the maximum torqueto release of the application of the torque is also divided into thefirst decrease period and the second decrease period, and the decreaserate of the warning torque in the first decrease period is set largerthan that in the second decrease period, whereby it is feasible toterminate the application of the warning torque, without causing thedriver to have a great uncomfortable feeling.

The driving operation support system can also be configured in such aform that an absolute rate of increasing the warning torque in the firstincrease period is smaller than an absolute rate of decreasing thewarning torque in the first decrease period.

In this configuration, the driving operation support system isconfigured in such a form that the absolute rate of increasing thewarning torque in the first increase period is smaller than that ofdecreasing the warning torque in the first decrease period, whereby itis feasible to secure a sufficient deviation margin time and to informthe driver of a start of the deviation prevention support by change ofthe steering torque. In addition, it is also feasible to reduce thedriver's uncomfortable feeling due to sudden decrease of the warningtorque and to moderately resolve the behavior of the vehicle afteroccurrence of the warning torque before nullification of the warningtorque.

Furthermore, the driving operation support system can also be configuredin such a form that a process of preventing the lane deviation by theapplication of the warning torque is set to be terminated by a steeringoperation and that when the process is terminated by the steeringoperation, the torque is decreased at the rate of decreasing the torquein the second decrease period from the start of the decrease.

During the driver's steering operation, the driver is alreadymanipulating the steering wheel in the direction to return the vehicleon the lane, without need for quickly decreasing the warning torque, andthere is no friction component in the steering mechanism. In this case,therefore, there is no need for setting the first decrease period.Therefore, the setting of the first decrease period is canceled todecrease the waning torque without quick decrease thereof.

As described above, the driving operation support system according tothe present invention achieves the lane deviation prevention controlwhile decreasing the behavior change felt by the driver during thecontrol in the low vehicle speed range, securing the deviation margintime and driver's reaction time, and improving the feeling about thewarning torque.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a driving operation support systemaccording to the present invention;

FIG. 2 is a front view of a meter unit;

FIG. 3 is a flowchart showing a control procedure of the drivingoperation support system according to the present invention;

FIG. 4 is an illustration for explaining travel paths of a vehicle withand without deviation prevention support in the vehicle running on aroad;

FIG. 5 is a graph showing an example of a wave pattern of applied torquein the deviation prevention support;

FIG. 6(a) is a graph showing an example of setting of applied torquewhere the applied torque is constant regardless of vehicle speed, FIG.6(b) a graph showing the relationship between vehicle speed and yaw ratein the forgoing setting, and FIG. 6(c) a graph showing the relationshipbetween vehicle speed and lateral acceleration in the foregoing setting;

FIG. 7(a) is a graph showing an example of setting of applied torquewhere the applied torque is increased with increase in vehicle speed,FIG. 7(b) a graph showing the relationship between vehicle speed and yawrate in the forgoing setting, and FIG. 7(c) a graph showing therelationship between vehicle speed and lateral acceleration in theforegoing setting;

FIG. 8(a) is a graph showing an example of setting of applied torquewhere the applied torque is increased with increase in vehicle speed andwhere an upper limit is set for the applied torque, FIG. 8(b) a graphshowing the relationship between vehicle speed and yaw rate in theforgoing setting, and FIG. 8(c) a graph showing the relationship betweenvehicle speed and lateral acceleration in the foregoing setting;

FIG. 9 is a graph showing a temporal change of applied torque in thedriving operation support system according to the present invention, incomparison with that in the conventional system;

FIG. 10 is a graph showing the relationship of applied torque againstlateral acceleration, used in setting of an initial value of appliedtorque;

FIG. 11 is a flowchart showing a procedure after a start of a process inan applied torque decrease interval;

FIG. 12 is a graph showing a temporal change of applied torque in theprocess shown in FIG. 11; and

FIG. 13 is an illustration for explaining travel paths of a vehicle withand without setting of a quick decrease range of applied torque in theapplied torque decrease interval.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE PRESENT INVENTION

The preferred embodiment of the present invention will be describedbelow with reference to the drawings. FIG. 1 is a block diagram of adriving operation support system according to an embodiment of thepresent invention.

As shown in FIG. 1, driving operation support system 1 according to thepresent embodiment is equipped with deviation prevention support ECU(Electric Control Unit) 10. Connected to the deviation preventionsupport ECU 10 are a vehicle speed detector 11, a steering torquedetector 12, a boundary-line recognition camera 13, a brake switch 14, aturn signal switch 15, and a main switch 16. Also connected to the ECU10 are a steering torque applier 17, a warning buzzer 18, and a meter19.

The deviation prevention support ECU 10 estimates whether the hostvehicle will deviate from the lane, based on information outputted fromthe vehicle speed detector 11, from the steering torque detector 12,from the boundary-line recognition camera 13, and so on. When the ECUresults in estimating that the host vehicle will deviate from the laneafter a predetermined time, it outputs a predetermined signal to thesteering torque applier 17, to the warning buzzer 18, and so on. Themore detailed functions of the deviation prevention support ECU 10 willbe described later.

The vehicle speed detector 11 is composed, for example, of sensorsattached to the front wheel portions of the vehicle, which detect thespeeds of the wheels to determine the vehicle speed during driving ofthe host vehicle. The vehicle speed detector 11 outputs the detectedvehicle speed to the deviation prevention support ECU 10.

The steering torque detector 12 is, for example, a detector attached toa steering rod connected to the steering wheel manipulated by the driverin the vehicle interior, and detects the steering torque exerted on thesteering wheel by driver's steering operation. The steering torquedetector 12 outputs the detected steering torque to the deviationprevention support ECU 10.

The boundary-line recognition camera 13 is, for example, a cameralocated at a position in the vehicle interior where it can view thecircumstances outside and in front of the vehicle from the upper part ofthe windshield, and takes an image of the circumstances outside thevehicle through the windshield. The boundary-ine recognition camera 13outputs the image of the exterior circumstances thus taken, to thedeviation prevention support ECU 10.

The brake switch 14 is, for example, a switch attached to a brake pedalmanipulated by the driver in the car interior, and detects a driver'soperation on the brake pedal. The brake switch 14 outputs a brake signalto the deviation prevention support ECU 10 when the driver depresses thebrake pedal to apply the brakes on the vehicle.

The turn signal switch 15 is, for example, a switch attached to a turnsignal lever manipulated by the driver in the vehicle interior, anddetects a driver's operation on the turn signal lever. The turn signalswitch 15 outputs a turn indication signal to the deviation preventionsupport ECU 10 when the driver manipulates the turn signal lever to givea turn signal.

The main switch 16 is, for example, a switch attached at a positionwhere the driver can set it in the vehicle interior, e.g., inside thedoor on the driver side. When the driver turns the main switch 16 on,the main switch 16 outputs an on signal to the deviation preventionsupport ECU 10. Receiving this on signal, the deviation preventionsupport ECU 10 initiates the deviation prevention support.

The steering torque applier 17 is, for example, an electric motor in anelectric power steering system connected to the steering rod of thesteering system. The steering torque applier 17 applies a predeterminedsteering torque being a warning torque of the present invention, to thesteering rod, based on an application signal outputted from thedeviation prevention support ECU 10. In the present specification, thesteering torque applied by the steering torque applier 17 is referred toas an applied torque.

The warning buzzer 18 is, for example, a buzzer disposed in theinstrument panel part in the vehicle interior, and emits a warning in apredetermined sound volume enough to reach the driver. The warningbuzzer 18 is provided with multiple types of signals, and issues apredetermined type of warning, based on a warning signal outputted fromthe deviation prevention support ECU 10.

The meter 19 is provided with a speed meter 21 and a tachometer 22, asshown in FIG. 2. The display part of the speed meter 21 providesdisplays of deviation prevention support execute indication 23 expressedby letters of “LKA” (lane keep assist), steering control executeindication 24, boundary-line recognition indication 25, radar cruiseindication 26, radar cruise setting speed indication 27, and so on.These display portions provide appropriate displays, based on a displaysignal outputted from the deviation prevention support ECU 10.

The operation or action of the driving operation support system 1 of thepresent embodiment having the above configuration will be describedbelow. The present embodiment is characterized by a pattern of theapplied torque by the steering torque applier 17 during execution of thelane deviation prevention, for performing the lane deviation preventionsupport, but the whole of the driving support control will be describedbefore the detailed description of this feature of the presentembodiment. FIG. 3 is a flowchart showing a control procedure of drivingoperation support system 1 according to the present embodiment.

In the driving operation support system 1 according to the presentembodiment, the deviation prevention support ECU 10 checks whether themain switch 16 is on, as a preliminary process to determine a start ofthe driving support. When the main switch 16 is on, a boundary-lineinformation process of extracting boundary-lines by image processingfrom an image taken by the boundary-line recognition camera 13 iscarried out to recognize boundary-lines of a lane on which the hostvehicle is running. Then a boundary-line recognition process is carriedout and a flag process is carried out based on the result of thedetection of boundary-lines. After execution of the boundary-lineinformation process, it is determined whether it is necessary to performsteering support (S1). The determination on whether it is necessary toperform the steering support is carried out based on the vehicle speedinformation outputted from the vehicle speed detector 11, theinformation on whether boundary-lines are recognized by the boundary-ineinformation process, and so on.

After the determination is made on whether it is necessary to performthe steering support, a evaluation of driver's operation is then made(S2). The evaluation of driver's operation is carried out based on thesteering torque signal from the steering torque detector 12, the brakesignal from the brake switch 14, the turn indication signal from theturn signal switch 15, and so on. When the steering torque signalindicates a value over a predetermined torque level, it is determinedthat the driver manipulated the steering wheel. When the brake switch 14outputs the brake signal, it is determined that the driver performed thebraking operation. When the turn signal switch 15 outputs the turnindication signal, it is determined that the driver manipulated the turnsignal lever. Whether the driving support is to be continued isdetermined based on the results of determinations on these driver'soperations.

After the evaluation of driver's operation is made an operation amountof deviation alleviation control is subsequently calculated (S3).Calculated herein is a target torque necessary for returning the hostvehicle to the inside of the lane. The operation amount of deviationalleviation control is calculated using a turning radius of the hostvehicle determined based on the steering wheel angle of the steeringwheel, and the vehicle speed of the host vehicle. A predetermined upperlimit is set for the operation amount of deviation alleviation control.The calculation of the deviation alleviation control operation amountwill be further described later.

After the calculation of the deviation alleviation control operationamount, an evaluation of deviation from the lane is made (S4). It isdetermined herein whether the host vehicle will deviate from the laneafter passage of a predetermined time, e.g., approximately one secondlater, and, based on the result of the evaluation on the deviation fromthe lane, it is determined whether activation of the steering torqueapplier 17 and others are to be demanded. The evaluation on thedeviation from the lane is made based on the state of necessity for thesteering support, the state of detection of boundary-lines, an offsetamount of the host vehicle relative to the lane, the yaw angle,estimated R of the road, the lane width, and so on.

Now, let us suppose that the host vehicle M is running on a road R, asshown in FIG. 4. A travel arrival position of the host vehicle M aboutone second later is calculated based on the speed of the host vehicle M,the yaw angle, the offset amount relative to the road R, and so on. Whenit is determined based on the result of the calculation that a travelpath C1 of the host vehicle M up to arrival at the travel arrivalposition is on a boundary-line W, the steering torque applier 17 appliesthe applied torque in the magnitude calculated in a subsequent process,to change the path, for example, to a travel path C2. The control isperformed so as to change the travel path in this manner. This change ofthe travel path from C1 to C2 lengthens the deviation margin time beforea deviation of the vehicle from the boundary-line. The application ofthe applied torque to the steering wheel notifies the driver of a riskof the deviation, to encourage the driver himself or herself to performan operation to prevent the lane deviation.

After evaluation of the deviation from the lane, a target torque ofdeviation alleviation control is calculated (S5). At this step, the ECUcalculates a wave pattern of the applied torque actually applied by thesteering torque applier 17 in accordance with the deviation alleviationoperation amount. The wave pattern of the applied torque at this timewill be further described later.

After the calculation of the deviation alleviation control targettorque, a horning buzzer process is carried out for informing the driverof execution of the deviation prevention support (S6). When theevaluation of deviation from the lane process results in determiningthat the host vehicle will deviate from the lane and when the steeringtorque applier 17 applies the applied torque, the waning buzzer 18outputs a warning of predetermined sound.

In conjunction with the execution of the homing buzzer process, awarning display process is carried out (S7). When the evaluation ofdeviation from the lane process results in determining that the hostvehicle will deviate from the lane and when the steering torque applier17 applies the applied torque, the meter 19 provides the displays ofdeviation prevention support execute indication 23, boundary-linerecognition indication, and so on.

After that, a predetermined data output process is carried out (S8),thereby completing the driving support.

Next, the time-varying wave pattern of the applied torque applied by thesteering torque applier 17 will be described. The deviation preventionsupport ECU 10 of the present embodiment outputs an applied torquesignal of a time-varying wave pattern, for example as shown in FIG. 5,to the steering torque applier 17, and the steering torque applier 17applies the applied torque to the steering rod, thereby applying thesteering torque on the steered wheels.

In the time-varying wave pattern shown in FIG. 5, the applied torque isincreased at a constant rate in an interval from a start of thedeviation prevention support up to reach the maximum applied torque(Start interval). After reaching the maximum applied torque, the appliedtorque is kept constant for a while (Keep interval). Thereafter, wherean application end condition is met, the applied torque is decreased(Close interval) for a while, and thereafter the applied torque isreduced at a smaller decrease rate up to 0. Thereafter, the process isterminated (Freeze interval). Concepts about the setting of thetime-varying wave pattern of the applied torque will be individuallydescribed below.

For preparing the wave pattern of the applied torque as described above,the maximum applied torque is first determined. The maximum appliedtorque is determined as the deviation alleviation control operationamount according to the vehicle speed of the host vehicle and others atthe step S3 in the flowchart shown in FIG. 3. If the maximum appliedtorque is constant independent of the vehicle speed, there will arise noparticular problem in terms of the steering feeling and the vehiclebehavior in the high vehicle speed range even if the maximum appliedtorque is relatively large. However, if the same maximum applied torqueas the maximum applied torque of the magnitude causing no problem in thevehicle behavior in the high vehicle speed range is applied in the lowvehicle speed range, the driver will feel the vehicle behavior changelarge, so as to cause a problem in terms of the steering feeling.

For example, let us consider a case where the maximum applied torque isconstant independent of the vehicle speed, as shown in FIG. 6(a). Inthis case, the vehicle speed is inversely proportional to the yaw ratecaused by the vehicle speed and applied torque, as shown in FIG. 6(b),and the lateral acceleration is constant independent of the vehiclespeed, as shown in FIG. 6(c). Therefore, with increase in the vehiclespeed, the lateral acceleration is invariant, whereas the yaw ratedecreases. This decrease of the yaw rate is considered to inducedriver's uncomfortableness of the steering feeling.

In order to alleviate such uncomfortableness, the maximum applied torqueis set according to the vehicle speed. Specifically, the maximum appliedtorque is set according to the vehicle speed so that the maximum appliedtorque is increased with increase in the vehicle speed, whereby it isfeasible to reduce the driver's uncomfortableness during execution ofthe lane deviation prevention support.

Particularly, in application of the maximum applied torque, a preferredsetting is such that the yaw rate on the vehicle becomes constantindependent of the vehicle speed. Let us suppose that the maximumapplied torque is set to increase with increase in the vehicle speed, asshown in FIG. 7(a). In setting the maximum applied torque in thismanner, it is preferable to set the maximum applied torque so that theyaw rate due to the applied torque becomes constant independent of thevehicle speed, as shown in FIG. 7(b).

When the maximum applied torque is set so that the yaw rate is constantindependent of the vehicle speed, the lateral acceleration variesaccording to the vehicle speed, so that the lateral acceleration can beincreased with increase in the vehicle speed, as shown in FIG. 7(c).Therefore, it is feasible to further reduce the driver'suncomfortableness during the application of the applied torque.

Incidentally, where the maximum applied torque is increased withincrease in the vehicle speed, the difference between the maximumapplied torque and the real vehicle behavior can be prevented frombecoming too large in the low to middle-high vehicle speed range of50-100 km/h. In this case, however, the lateral acceleration, i.e., thereal vehicle behavior will become too large in the high vehicle speedrange over the foregoing low to middle-high speed range, so as topossibly cause driver's uncomfortableness.

For setting the maximum applied torque, therefore, an upper limit is setfor the vehicle speed in the change of the maximum applied torqueaccording to the vehicle speed. This upper limit is determined, forexample, according to a reference vehicle speed. Specifically, duringexecution of the deviation prevention support at vehicle speeds not morethan the reference vehicle speed set as the upper limit, as shown inFIG. 8(a), the maximum applied torque is changed according to thevehicle speed so that the maximum applied torque is increased withincrease in the vehicle speed, whereby the yaw rate due to the appliedtorque becomes constant, as shown in FIG. 8(b). On the other hand,during execution of the deviation prevention support at vehicle speedsover the reference vehicle speed, the maximum applied torque isconstant. When the maximum applied torque is kept constant, the yaw ratedecreases, but the lateral acceleration is constant, as shown in FIG.8(c), so as to reduce the difference between steering torque and actualvehicle behavior.

By setting the maximum applied torque in this manner, the driver'suncomfortableness due to the decrease of the yaw rate can be relieved inthe low vehicle speed range. The driver's uncomfortableness due to thedifference between steering torque and actual vehicle behavior can alsobe relieved in the high vehicle speed range.

Next, the deviation alleviation control target torque calculated at stepS5 in the flowchart shown in FIG. 3 will be described. Set herein aretime-varying wave patterns of the applied torque up to reaching themaximum applied torque and from the maximum applied torque to theapplied torque of 0. The time-varying wave patterns of the appliedtorque are set based on the maximum applied torque and others.

For example, let us suppose that a basic pattern of the applied torqueis set as indicated by a thin line L1 in FIG. 9. In the operation ofchanging the applied torque to the maximum applied torque correspondingto the vehicle speed in accordance with the basic pattern of this form,if a rate of change up to the maximum applied torque and a rate ofchange in decrease from the maximum applied torque are kept eachconstant and if the maximum applied torque becomes over the basicpattern, as indicated by a dashed line L2 in FIG. 9, a rise time (a timefrom a start of applying torque up to reach the maximum applied torque)and a fall time (a time from a start of decrease of torque at themaximum applied torque to an end of applying torque) will both becomelong.

The increase of the rise time will result in lengthening the time beforeoccurrence of aimed vehicle behavior. This will result in failing tosecure a sufficient deviation margin time in the high vehicle speedrange. The increase of the fall time will result in failing to quicklyterminate the control after an end of the operation necessary for thedeviation prevention support, so as to cause driver's uncomfortableness.

For solving this problem, a rate of increasing the applied torque duringthe rise is so set that the time up to reach the maximum applied torqueis set to a predetermined constant time, e.g., 0.4 sec, as indicated bya solid line L3 in FIG. 9. By setting the rate of increasing the appliedtorque up to reach the maximum applied torque in this manner, it isfeasible to keep constant the time from the start of applying torque upto reach the maximum applied torque. This makes it feasible to shortenthe time up to occurrence of the aimed vehicle behavior. Therefore, asufficient deviation margin time can be secured even in the high vehiclespeed range. Since after the start of the deviation prevention supportthe large applied torque is applied in the high speed range, the drivercan be informed through the steering wheel that the present status is adangerous situation where the vehicle will deviate from the lane.

Just as in the case of the change rate during the rise, a rate ofdecreasing the applied torque during the fall from the start of decreasefrom the maximum applied torque up to the end of application is also setbased on the maximum applied torque. For example, a rate of decreasingthe warning torque is so set that a time from the start of decrease fromthe maximum applied torque up to the end of application becomes a secondpredetermined time. Supposing the rise time of applied torque is set toa first predetermined time, the second predetermined time as the falltime is desirably set to be longer than the first predetermined time.This setting achieves the following advantages: during the rise awarning can be quickly issued after it is determined that the warning isnecessary; during the fall it is feasible to alleviate the driver'suncomfortableness due to quick variation of applied torque.

Once the rate of increasing the applied torque during the rise isdetermined, the rate of decreasing the applied torque during the fallcan also be considered to be determined so as to reduce the appliedtorque at the same absolute rate as the rate of increasing the appliedtorque during the rise. However, if the applied torque is decreased atthe same absolute rate as the rate of increasing the applied torqueduring the rise, the applied torque will suddenly become null in thehigh speed range, so as to change the steering load. This makes thedriver feel uncomfortable.

For this reason, during the fall from the maximum applied torque, theapplied torque is decreased at the rate whose absolute value is smallerthan the rate of increasing the applied torque during the rise, asindicated by the solid line L3 in FIG. 9. Specifically, for example, thechange rate is set so that the fall time becomes 0.6 sec.

By decreasing the applied torque at the rate whose absolute value issmaller than the rate of increasing the applied torque during the risein this manner, it is feasible to alleviate the driver'suncomfortableness and to moderately resolve the behavior of the vehicle.Accordingly, it is feasible to achieve the objectives of securing thedeviation margin time during the rise and resolving driver'suncomfortableness during the fall, at once.

On the other hand, on the occasion of starting the deviation preventionsupport, the system is required to notify the driver under driving ofthe start of the deviation prevention support in an early stage and withcertainty. In notifying the driver of the deviation prevention support,a secure method is to make the driver feel the applied torque. For thisreason, upon the start of the deviation prevention support, the systemis demanded to make the driver fast feel the applied torque. In thedeviation prevention support, in order to secure the deviation margintime, the system is also required to start the vehicle behavior for thedeviation prevention support in an early stage.

For meeting these demands, the initial value of applied torque isdetermined based on the friction property of the steering mechanism. Ifthe applied torque by the deviation prevention support is not more thanthe friction amount of the steering system due to the friction propertyof the steering mechanism, the driver will not feel the applied torque.When the applied torque exceeds the friction amount of the steeringsystem, the driver comes to feel the applied torque. When the appliedtorque exceeds the friction amount of the steering system, the vehiclebehavior for the deviation prevention support appears.

For this reason, a real characteristic between steering torque andlateral acceleration in the host vehicle is determined to obtain a realcharacteristic curve P1, as shown in FIG. 10. A tangent P2 to this realcharacteristic curve P1 is determined, and an intersection is obtainedbetween the tangent P2 and a line at the lateral acceleration of 0. Atorque value X indicated at this intersection is defined as a frictioncompensation amount, and is set as an initial value of the appliedtorque. In the present embodiment the specific torque is set as theinitial value, but the applied torque may be arranged to quicklyincrease in an early stage by setting a certain time range (referred toas a first increase period) and setting a torque increase rate larger inthe first increase period than that in a second torque increase periodsubsequent to the first increase period. The case where the specifictorque (not being 0) is set as the initial value is equivalent to a casewhere in the actual control the first increase period is reduced to atime step length of the control.

By setting the initial value of the applied torque in this manner, it isfeasible to notify the driver of the start of the deviation preventionsupport in the early stage by making the driver feel the applied torque.It is also feasible to make the host vehicle quickly start the vehiclebehavior for the deviation prevention support.

On the other hand, in the decrease of the applied torque from themaximum, the system is demanded to quickly decrease the applied torqueto 0. However, if the applied torque is reduced to 0 at once, the quickelimination of the applied torque can result in making the driver feeluncomfortable, and thus the system is required to resolve suchuncomfortableness. When the host vehicle returns into the lane withoutthe vehicle behavior for the deviation prevention support for somereason of the applied torque being relatively strong and disturbancebeing small, the system is required to reduce the deflection angle ofthe vehicle.

For meeting these demands, the applied torque can also be quicklyreduced by the degree equivalent to the friction amount of the steeringsystem during the decrease of the applied torque from the maximum. Thefriction of the steering system herein acts in the opposite direction tothat in the increase case of the applied torque so as to cancel theapplied torque. Therefore, the friction compensation amount isdetermined to be a torque quantity 2X which is double the torquequantity X shown in FIG. 10. A period where the applied torquecorresponding to the friction compensation amount is decreased isdefined as a quick decrease range (first torque decrease period), and adecrease rate is set larger in the first torque decrease period thanthat in a second decrease period subsequent to the first torque decreaseperiod. In this quick decrease range, even if the applied torque isquickly decreased, it is canceled out by the steering friction, and thedecrease of force actually acting on the steered wheels is small.Therefore, the driver is unlikely to feel uncomfortable with thedecrease of the applied torque. In addition, the deflection angle of thevehicle can be made small even if the vehicle behavior for deviationprevention support is not carried out.

The application of the applied torque by the steering torque applier 17is terminated when a predetermined application end condition is met. Theapplication end condition is one of a steering operation, a brakingoperation, a turn signal operation, an operation of turning the mainswitch off in failure, a return from a lane deviation state, and so on.The steering operation, the braking operation, the turn signaloperation, and the main switch off operation in failure are determinedbased on input signals from the steering torque detector 12, from theturn signal switch 15, from the brake switch 14, and from the mainswitch 16, respectively. The return from the lane deviation state isdetermined based on arithmetic processing in the deviation preventionsupport ECU 10.

When the driver's steering operation among these terminates theapplication of the applied torque, there is no friction amount of thesteering system. Therefore, when the application of the applied torqueis terminated by the driver's steering operation, the quick decreaserange of applied torque is not set, and the applied torque is notquickly decreased but is decreased to 0 without setting the quickdecrease range of applied torque.

A procedure after a start of the applied torque decrease process will bedescribed below. FIG. 11 is a flowchart showing the procedure after thestart of the applied torque decrease interval process.

After a start of the applied torque decrease interval process, it isdetermined as to a shift into the applied torque decrease intervalprocess that the shift into the applied torque decrease interval processwas made by a steering operation (S11). When the result is that theshift was made into the applied torque decrease interval by any endcondition other than the steering operation, a torque decrease processwith a steep slope is carried out (S12).

In this case, as indicated by a solid line Q1 in FIG. 12, the appliedtorque decrease process with a steep slope is first carried out in anapplied torque decrease interval (Close interval). In the applied torquedecrease process with the steep slope, the range of the friction amountof the steering system is set as a quick decrease range, and the appliedtorque is quickly decreased in this quick decrease range. By quicklydecreasing the applied torque in this manner, it is feasible to reducethe applied torque to 0 in an early stage, without causing driver'suncomfortableness.

After completion of the quick decrease process of the applied torque inthe quick decrease range, a torque decrease process with a gentle slopeis then carried out (S13). In the applied torque decrease process withthe gentle slope, the applied torque is decreased at a change rate notto cause driver's uncomfortableness even during the decrease of theapplied torque.

On the other hand, when it is determined at step S11 that the shift wasmade into the applied torque decrease interval process by the steeringoperation, there is no friction amount of the steering system by virtueof the steering operation. In this case, as indicated by a dashed lineQ2 in FIG. 12, the applied torque is decreased at the gentle slope fromthe maximum applied torque (S13), without setting the quick decreaserange. In this way, the process in the applied torque decrease intervalis completed.

When the quick decrease range is set in the applied torque decreaseinterval process as described above, the applied torque decrease processcan be performed within a short time, with little driver'suncomfortableness in the vehicle behavior and steering. When the quickdecrease range is set, the angle between the direction of the hostvehicle after completion of the control and a boundary-line W on theroad R becomes a vehicle deflection angle θA, for example, as indicatedby a solid line in FIG. 13. In contrast to it, if the quick decreaserange is not set, the angle between the direction of the host vehicleafter completion of the control and the boundary-line W on the road Rbecomes a vehicle deflection angle θB, for example, as indicated by adashed line in FIG. 13. The vehicle deflection angle θA with setting ofthe quick decrease range is smaller than the vehicle deflection angle θBwithout setting of the quick decrease range. Therefore, where the quickdecrease range is set, the vehicle deflection angle after completion ofthe control becomes smaller, so that the vehicle can return to the laneat the angle closer to the direction along the lane.

Based on the above concepts, the time-varying wave pattern of theapplied torque shown in FIG. 5, which is the deviation alleviationcontrol target torque at step S5 in the flowchart shown in FIG. 3, isset as described below.

The time-varying wave pattern of applied torque is composed of fourintervals of the Start interval, the Keep interval, the Close interval,and the Freeze interval. First, the time-varying wave pattern in theKeep interval is determined based on the maximum applied torquedetermined at step S3. In the Keep interval, the applied torque of themaximum applied torque is kept applied. The continuation time of theKeep interval is determined by calculating a time from a lane deviationstate to a return, based on the vehicle speed, the vehicle width, theoffset amount of the host vehicle, and so on. However, where theapplication end condition is one except for the return from the lanedeviation state, a shift is made into the Close interval at a point oftime when the application return condition is met.

After the setting of the Keep interval, the initial value of the appliedtorque in the Start interval is set. The initial value of the appliedtorque is set as follows: the torque quantity X shown in FIG. 10, whichis the steering system friction amount determined based on the frictionproperty of the steering mechanism, is set as the initial value ofapplied torque as it is. When the steering system friction amount is setas the initial value of applied torque, the vehicle behavior fordeviation prevention appears in an early stage, whereby the driver canfeel the applied torque.

Since the continuation period of the Start interval is determined to bea fixed time, e.g., 0.4 sec, the rate of increasing applied torque inthe Start interval is then determined based on the initial value ofapplied torque and the maximum applied torque. The applied torque isincreased at this rate. Since the continuation period of the Startinterval is set at the fixed time, a sufficient deviation margin timecan be secured even in the high vehicle speed range.

Subsequently, the time-varying wave pattern in the Close interval isdetermined. In the Close interval, the time-varying wave pattern isdetermined according to the flowchart shown in FIG. 12. When the shiftinto the Close interval is made by a condition except for the steeringoperation, the quick decrease range is set, and the time-varying wavepattern to quickly decrease the applied torque is set during the periodof decrease of the applied torque equivalent to the steering systemfriction amount. After the decrease of the applied torque equivalent tothe steering system friction amount, the wave pattern is determined soas to decrease the applied torque at the rate not to cause driver'suncomfortableness even with the decrease of the applied torque. In thismanner, the application of the applied torque can be terminated in anearly stage, without causing driver's uncomfortableness.

On the other hand, where the shift into the Close interval is made bythe steering operation, the quick decrease range is not set and thetime-varying wave pattern is set to decrease the applied torque at therate not to cause driver's uncomfortableness even with the decrease ofthe applied torque, though not shown in FIG. 5. This makes it feasibleto prevent the driver from feeling uncomfortable, even with decrease ofthe applied torque.

1. A driving operation support system for, when lane deviation estimating means estimates that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a deviation from lane, wherein a pattern of application of the warning torque to the vehicle is determined according to a vehicle speed.
 2. The driving operation support system according to claim 1, wherein the warning torque is increased with increase in the vehicle speed when estimating that the vehicle will deviate from the lane.
 3. The driving operation support system according to claim 1, wherein in the application of the warning torque to the vehicle, the warning torque is set in such a magnitude that a yaw rate on the vehicle is kept constant.
 4. The driving operation support system according to claim 2, wherein an upper limit is set for the warning torque applied to the vehicle.
 5. The driving operation support system according to claim 4, wherein the upper limit is the warning torque at a reference vehicle speed.
 6. The driving operation support system according to claim 1, wherein the warning torque increases to its maximum at a specified rate responsive to the maximum warning torque applied to the vehicle.
 7. The driving operation support system according to claim 6, wherein the rate of increasing the warning torque is so set that a time necessary to reach the maximum warning torque is kept constant.
 8. A driving operation support system for, when lane deviation estimating means estimates that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a lane deviation, wherein in an operation of, after increase of the warning torque, decreasing the warning torque increased, the warning torque is decreased at different absolute rate from that during the increase of the warning torque.
 9. The driving operation support system according to claim 8, wherein the absolute rate of increasing the warning torque is set larger than the absolute rate of decreasing the warning torque.
 10. A driving operation support system for, when lane deviation estimating means estimates that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a lane deviation, wherein in an operation of increasing the warning torque to a maximum, a rate of increasing the warning torque in a predetermined first increase period from a start of the increase is set larger than a rate of increasing the warning torque in a second increase period subsequent to the first increase period.
 11. The driving operation support system according to claim 10, wherein in an operation of decreasing the warning torque from the maximum, a rate of decreasing the warning torque in a predetermined first decrease period from a start of the decrease is set larger than a rate of decreasing the warning torque in a second decrease period subsequent to the first decrease period.
 12. The driving operation support system according to claim 11, wherein an absolute rate of increasing the warning torque in the first increase period is smaller than an absolute rate of decreasing the warning torque in the first decrease period.
 13. The driving operation support system according to claim 11, wherein a process of preventing the lane deviation by the application of the warning torque is set to be terminated by a steering operation, and wherein when the process is terminated by the steering operation, the torque is decreased at the rate of decreasing the torque in the second decrease period from the start of the decrease.
 14. A driving operation support system for, when lane deviation estimating means estimates that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a lane deviation, wherein in an operation of decreasing the warning torque from a maximum, a rate of decreasing the warning torque in a predetermined first decrease period from a start of the decrease is set larger than a rate of decreasing the warning torque in a second decrease period subsequent to the first decrease period.
 15. The driving operation support system according to claim 14, wherein a process of preventing the lane deviation by the application of the warning torque is set to be terminated by a steering operation, and wherein when the process is terminated by the steering operation, the torque is decreased at the rate of decreasing the torque in the second decrease period from the start of the decrease.
 16. The driving operation support system according to claim 1, wherein in an operation of, after increase of the warning torque, decreasing the warning torque increased, the warning torque is decreased at an absolute rate different from that during the increase of the warning torque.
 17. The driving operation support system according to claim 16, wherein the absolute rate during the increase of the warning torque is set larger than the absolute rate during the decrease of the warning torque.
 18. The driving operation support system according to claim 16, wherein in an operation of increasing the warning torque to a maximum, a rate of increasing the warning torque in a predetermined first increase period from a start of the increase is set larger than a rate of increasing the warning torque in a second increase period subsequent to the first increase period.
 19. The driving operation support system according to claim 16, wherein in an operation of decreasing the warning torque from a maximum, a rate of decreasing the warning torque in a predetermined first decrease period from a start of the decrease is set larger than a rate of decreasing the warning torque in a second decrease period subsequent to the first decrease period.
 20. A driving operation support method for, when estimating that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a deviation from lane, wherein a pattern of application of the warning torque to the vehicle is determined according to a vehicle speed.
 21. The driving operation support method according to claim 20, wherein the warning torque is increased with increase in the vehicle speed when estimating that the vehicle will deviate from the lane.
 22. The driving operation support method according to claim 20, wherein in the application of the warning torque to the vehicle, the warning torque is set in such a magnitude that a yaw rate on the vehicle is kept constant.
 23. The driving operation support method according to claim 21, wherein an upper limit is set for the warning torque applied to the vehicle.
 24. The driving operation support method according to claim 23, wherein the upper limit is the warning torque at a reference vehicle speed.
 25. The driving operation support method according to claim 20, wherein the warning torque increases to its maximum at a specified rate responsive to the maximum warning torque applied to the vehicle.
 26. The driving operation support method according to claim 25, wherein the rate of increasing the warning torque is so set that a time necessary to reach the maximum warning torque is kept constant.
 27. A driving operation support method for, when estimating that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a lane deviation, wherein in an operation of, after increase of the warning torque, decreasing the warning torque increased, the warning torque is decreased at different absolute rate from that during the increase of the warning torque.
 28. The driving operation support method according to claim 27, wherein the absolute rate of increasing the warning torque is set larger than the absolute rate of decreasing the warning torque.
 29. A driving operation support method for, when estimating that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a lane deviation, wherein in an operation of increasing the warning torque to a maximum, a rate of increasing the warning torque in a predetermined first increase period from a start of the increase is set larger than a rate of increasing the warning torque in a second increase period subsequent to the first increase period.
 30. The driving operation support method according to claim 29, wherein in an operation of decreasing the warning torque from the maximum, a rate of decreasing the warning torque in a predetermined first decrease period from a start of the decrease is set larger than a rate of decreasing the warning torque in a second decrease period subsequent to the first decrease period.
 31. The driving operation support method according to claim 30, wherein an absolute rate of increasing the warning torque in the first increase period is smaller than an absolute rate of decreasing the warning torque in the first decrease period.
 32. The driving operation support method according to claim 1, wherein a process of preventing the lane deviation by the application of the warning torque is set to be terminated by a steering operation, and wherein when the process is terminated by the steering operation, the torque is decreased at the rate of decreasing the torque in the second decrease period from the start of the decrease.
 33. A driving operation support method for, when estimating that a moving vehicle will deviate from a lane, applying a warning torque to the vehicle to prevent a lane deviation, wherein in an operation of decreasing the warning torque from a maximum, a rate of decreasing the warning torque in a predetermined first decrease period from a start of the decrease is set larger than a rate of decreasing the warning torque in a second decrease period subsequent to the first decrease period.
 34. The driving operation support method according to claim 1, wherein a process of preventing the lane deviation by the application of the warning torque is set to be terminated by a steering operation, and wherein when the process is terminated by the steering operation, the torque is decreased at the rate of decreasing the torque in the second decrease period from the start of the decrease.
 35. The driving operation support method according to claim 19, wherein in an operation of, after increase of the warning torque, decreasing the warning torque increased, the warning torque is decreased at an absolute rate different from that during the increase of the warning torque.
 36. The driving operation support method according to claim 35, wherein the absolute rate during the increase of the warning torque is set larger than the absolute rate during the decrease of the warning torque.
 37. The driving operation support method according to claim 35, wherein in an operation of increasing the warning torque to a maximum, a rate of increasing the warning torque in a predetermined first increase period from a start of the increase is set larger than a rate of increasing the warning torque in a second increase period subsequent to the first increase period.
 38. The driving operation support system according to claim 35, wherein in an operation of decreasing the warning torque from a maximum, a rate of decreasing the warning torque in a predetermined first decrease period from a start of the decrease is set larger than a rate of decreasing the warning torque in a second decrease period subsequent to the first decrease period. 